For glass and most plastics, about 4-5% of incident light is reflected from the surface. To eliminate disturbance of the external light and increase light transmission to enhance the clarity of display images and the performance of optical components, antireflective and antiglare technologies are usually applied in liquid crystal displays (LCD) or touch panels to prevent the deterioration of visibility by reflective light. However, antiglare technologies are more popular in practical display applications due to cost considerations. An antiglare film comprises three major components: light-scattering particles, binding resin, and a substrate. Similar to LCD diffusers, the light-scattering particles are used to scatter the incident light via the difference in refractive indices between particles/air or particles/resin. Antiglare films are fabricated by coating a solution of light-scattering particles and binding resin on a substrate. After solvent evaporation, the surface of the coating layer becomes rough and uneven due to the light-scattering particles. The haze caused by the surface roughness is called outer haze. On the contrary, the inner haze is caused by the difference in refractive indices of the particles and that of the resin. The inner haze and the outer haze compose the total haze. In applications of LCD diffusers, only the total haze is taken into account. The goal of diffusers is to homogenize the scattering light from the light sources or the light guide plate in a two-dimensional fashion and avoid the occurrence of locally concentrated light. The effect of light homogenization is enhanced when either the inner or outer haze is increased. The surrounding light reflected from the surface of the antiglare film, so the glare was mostly suppressed by the outer haze. The inner haze of the antiglare film will improve the glare of the light emitted from the interior of the display when viewed with the naked eye. The function of the inner haze is similar to the LCD diffuser. Although the outer haze is also helpful to decrease the glare of the light emitted from the interior of the display, the image on the display becomes whitish, and the black density decreases with increasing outer haze. Therefore, the design of the inner and outer hazes of an antiglare film is important to display technologies and more complicated than that of a diffuser.
FIG. 1 shows the structure of a conventional antiglare film. The antiglare film structure comprises a substrate 1 and an antiglare coating layer 2 coated on the substrate 1. The antiglare coating layer 2 further comprises a resin 3 and light-scattering particles 4. In fabricating the antiglare film, an antiglare coating solution is coated on the substrate 1, and the coated film is then placed in an oven to evaporate the solvent in the antiglare coating solution. After that, the coated film is treated with ultraviolet light or placed in an oven to cure the resin 3 in the antiglare coating solution, whereby the antiglare coating layer 2 is formed. When the antiglare coating solution is initially coated on the substrate 1, the light-scattering particles 4 are uniformly distributed in the antiglare coating solution. When the solvent is being vaporized, the resin 3 and the light-scattering particles 4 gradually deposit on the substrate 1 to form the antiglare coating layer 2. When the solvent is being vaporized, the interaction between the solvent and the resin 3, the interaction between the solvent and the light-scattering particles 4, and the interaction between the resin 3 and the light-scattering particles 4 are very complicated. It results that the light-scattering particles 4 are randomly distributed in antiglare layer 2. Therefore, the conventional technology can not control the distribution of the light-scattering particles 4, leading to the variation on the ratio of outer haze to inner haze of the antiglare film.
Although the configuration of an antiglare film is simple and products have been commercialized recently by Japanese manufactures (Dai Nippon Printing Co., Ltd., Nitto Denko Corp., Fuji Photo Film Co., Ltd., Tomoegawa Paper Co., Ltd., and Lintec Corp.), the ratio of outer haze to inner haze is not easily controlled. Some patents, such as U.S. Pat. No. 5,998,013 “Anti-glare Hard Coat Film and Process for Producing the Film”, U.S. Pat. No. 6,217,176 “Antiglare Film and Use Thereof”, U.S. Pat. No. 6,613,426 “Very fine anti-glare hard coat film”, U.S. Pat. No. 6,696,140 “Anti-glare Film and Process for Producing Same Thereof”, U.S. Pat. No. 6,896,960 “Anti-glare hard coat film”, U.S. Pat. No. 7,033,638 “Antiglare Film and Process for Producing the Same”, Taiwan patent No. 557363 “Antiglare Film”, Taiwan patent No. 590886 “Method for Fabricating Antiglare Film”, and Taiwan patent No. M252022 “Optical Antiglare Film”, have revealed that the inner haze and the outer haze can be controlled by the ratio of light-scattering particles to the binding resin, the difference in refractive indices of the light-scattering particles and the binding resin, the diameter of the light-scattering particles, and the thickness of the antiglare coating layer. More light-scattering particles, larger particle sizes, or thinner thickness of antiglare coating layer will cause a higher outer haze due to the formation of more significant concave and convex surfaces. On the other hand, larger differences in refractive indices of the light-scattering particles and the binding resin or thicker thickness of the antiglare coating layer will lead to the increase of inner haze.
In the conventional technologies, the antiglare coating solution must be reformulated if the haze of antiglare films is changed. However, the adjustment of these parameters may result in a significant limitation of the practical application due to the change of the wet-film thickness and the viscosity of the coatings.
Japan patent pub. No. 2006-088643 “Manufacturing Process of Embossed Roll” and U.S. Pat. No. 7,008,066 “Antiglare Film, Process for Producing the Same, and Display Device Using Antiglare Film” use an embossed roll to form micro-embossing on the coating to achieve an antiglare or antireflection effect. Although these methods can fabricate antiglare films with different hazes, different embossed rolls are needed for the different hazes, resulting in the increase of cost. Besides, the above-mentioned prior arts can not change the inner haze.